DE 197 54 431 A1, which is incorporated by reference, discloses a brake fluid reservoir having a filler neck protruding outwards from the housing and a strainer located in the filler neck. It is in the very nature of things that fine-meshed and correspondingly efficient strainers can decisively delay a fluid filling operation, so that without sanction these are often removed or left out. Safeguards are therefore proposed in order to prevent unsanctioned removal of the strainer. Other sources propose separate ventilation and venting apertures, which are intended to improve the rate of flow through the strainer. It is feasible, however, particularly in the case of very rapid and especially automated hydraulic filling operations, for the separate ventilation apertures to be inappropriately and inadmissibly used to bypass the strainer, so that unstrained fluid gets into the motor vehicle brake system.
One particular problem is that today's vehicle manufacturers want so-called vacuum filling on their assembly line. This high-vacuum filling requires an automatic filling unit having an adapter part which forms an airtight replacement for a pressure-balancing reservoir cap, a length of tube extending into the filler neck in order to create a vacuum throughout the entire brake system before fluid filling, and to automatically establish a defined fluid level in the brake system after fluid filling. This is basically achieved in that after the creation of a vacuum and the subsequent fluid filling (with an excess pressure of 1 bar, for example) and a further ensuing settlement phase any excess fluid is drawn off in order to establish a level. Removable filters are advantageous in order that the length of tube can be introduced into the reservoir to a sufficient depth even in the case of a small reservoir. Such filters have the associated disadvantage, however, that they can get lost or their fitting can be overlooked.